The kidneys are important regulators of blood pressure. They regulate circulatory volume by controlling sodium and water balance, thus maintaining extracellular fluid volume homeostasis. It is well established that the pathogenesis of salt-sensitive hypertension is caused by impaired sodium handling in the kidneys, but the critical factors leading to renal sodium retention remain unidentified. An important role for T cells in hypertension has been proposed in the past decade. However, no related feasible treatment options have been proposed, because the mechanisms underlying this role for T cells have not been elucidated. We recently identified a novel role for kidney-infiltrated CD8+ T cells (CD8Ts) in enhancing salt retention; renal infiltrated CD8Ts interact with distal convoluted tubule cells (DCTs), stimulating the sodium-chloride co- transporter (NCC) in the DCTs, resulting in elevation of blood pressure. These findings led us to hypothesize that the interaction between CD8Ts and renal tubular cells mediates T cell-homing to the kidney, which may represent a kidney defect that contributes to the pathogenesis of salt sensitive hypertension. In the proposed study, we will investigate the critical molecular determinants in the kidney, by which CD8Ts interact with renal tubular cells and determine how this kidney-homing mechanism of CD8Ts contributes to excessive salt retention, leading to high blood pressure. Specifically, Aim 1 will test our hypothesis that cytokines produced from activated CD8Ts prime DCTs to express co-signaling molecule, which initiates the interaction between DCTs and CD8Ts; Aim 2 will identify the adhesion molecules that mediate a putative immunological synapse between these two cell types. Aim 3 will determine the critical role of potassium channel Kir4.1 in CD8T- induced upregulation of NCC and possibly other sodium transporters in the distal nephron, leading to excessive salt retention and consequent elevation of blood pressure. Our preliminary studies have identified key molecules for each Aim. As proof of principle experiments, immunological neutralization or genetic deletion of these molecules in the kidneys of mice prevented stimuli-induced upregulation of NCC in the kidney and consequently lowered blood pressure. Complementary in vivo and in vitro studies are designed in this proposal to accomplish our aims. We will use kidney-specific knockout or knockdown methods in animals to determine the precise roles of key molecules in this study. Accomplishing our aims will elucidate the important molecular mechanisms regarding T cell homing to the kidney, thus impairing salt and volume homeostasis, and affecting blood pressure. We propose that salt-sensitive hypertension is caused, at least in part, by immune disorders in the kidney. Moreover, the key molecules identified in this study may represent novel targets for future immunotherapy against this prevalent health problem.